get some basic sampling going

1 files changed, 27 insertions, 0 deletions

diff --git a/kamon-core/src/main/scala/kamon/trace/Sampler.scala b/kamon-core/src/main/scala/kamon/trace/Sampler.scala
index a26e61be..491cf358 100644
--- a/kamon-core/src/main/scala/kamon/trace/Sampler.scala
+++ b/kamon-core/src/main/scala/kamon/trace/Sampler.scala
@@ -1,5 +1,32 @@
 package kamon.trace
 
 trait Sampler {
+  def decide(spanID: Long): Boolean
+}
+
+object Sampler {
+  val always = new Constant(true)
+  val never = new Constant(false)
+
+  def random(chance: Double): Sampler = {
+    assert(chance >= 0D && chance <= 1.0D, "Change should be >= 0 and <= 1.0")
+
+    chance match {
+      case 0D       => never
+      case 1.0D     => always
+      case anyOther => new Random(anyOther)
+    }
+  }
+
+  class Constant(decision: Boolean) extends Sampler {
+    override def decide(spanID: Long): Boolean = decision
+  }
+
+  class Random(chance: Double) extends Sampler {
+    val upperBoundary = Long.MaxValue * chance
+    val lowerBoundary = -upperBoundary
 
+    override def decide(spanID: Long): Boolean =
+      spanID >= lowerBoundary && spanID <= upperBoundary
+  }
 }